This invention relates to a borehole logging apparatus for deep well drilling, with a device for transmitting measured data obtained while drilling from a borehole through the drilling fluid to the earth's surface, with an elongated housing which is adapted for insertion in the drilling fluid conduit of a drill string, includes at its influx end an entrance opening leading into a central housing conduit and has, downstream from the entrance opening, a sealing ring effecting a seal against the drill string, which further includes a bypass opening arranged downstream from the sealing ring and leading from the central housing conduit into the drilling fluid conduit of the drill string, and, downstream from the bypass opening, has a passageway connecting the central housing conduit with the drilling fluid conduit of the drill string, said passageway being adapted to be throttled at least in part by a controllable closure element of a hydromechanical signal transmitter arranged in the housing, said closure element being repeatedly movable, at controlled intervals and in response to signals characteristic of measured data to be transmitted, from a passing position into a throttling position and back again into the passing position in order to generate in the drilling fluid a coded series of positive pressure pulses corresponding to the signals.
Apparatus of the type referred to are employed in particular in directional drilling in order to transmit measured data determined by measuring devices in the drill string while drilling to the earth's surface and, on the basis of such measured data, to permit the progress and direction of drilling to be influenced to the desired extent.
In a borehole logging apparatus of the type referred to which is known from DE 199 39 262 C1, fluid flow to the signal transmitter is through a central feed pipe arranged in the housing and surrounded by an exchangeable bypass ring, to which the entire drilling fluid current is fed through a filter pipe and through which part of the drilling fluid current is routed back to the drill string via bypass openings. By exchanging the bypass ring and, as the case may be, the feed pipe for parts having a different flow cross-section, this known apparatus is adaptable to different drill string diameters and flow velocities to be able to obtain in each case sufficiently significant pressure pulses for signal transmission. Each conversion necessitates however the removal of the borehole logging apparatus, which involves considerable expenditure of energy and time, with the attendant disadvantage of requiring a correspondingly long interruption of the drilling operation.